As produced at the wellhead, crude oils contain substantial quantities of water and inorganic particulates, and it has long been standard practice to require that the combined solids and water (BS&W) content be reduced to a value not exceeding a stated small percentage before the crude is introduced to a pipeline or supplied to a refinery. Such reduction of the BS&W content is necessary both to minimize damage to pipeline and refining equipment from, e.g., corrosion and abrasive wear, and to minimize losses arising from transporting and processing the non-petroleum constituents making up the BS&W content. Though specifications vary among localities and refineries, a typical specification requires that the BS&W content of the crude not exceed 0.5% by volume.
The BS&W content of many crudes can be brought within specifications simply and easily, as by gravitational separation and, when required, addition of various treating agents. However, the heavy oil crudes, and especially those produced by fireflooding or other thermal recovery practices, have presented a more serious problem and no completely satisfactory method has heretofore been available for reducing the BS&W content of such crudes. Such crudes are highly viscous, so that the raw crude must in all events be diluted with, e.g., a wide gasoline fraction, commonly called condensate, to achieve adequate fluidity for handling and treatment. Even thus diluted, however, simple settling operations, even for extended times, do not result in separation of the water from the oil, and it is commonly recognized that a substantial part of the remaining water is present as the disperse phase of a water-in-oil emulsion. Attempts to break the emulsions in such crudes have met with little success in many cases, and much attention has been given to the emulsion breaking problem by workers in the field. Heretofore, it has commonly been thought that, when the BS&W content of a heavy oil crude could not be brought within pipeline specifications, a primary cause was stabilization of the emulsion by very small particles of clay or the like distributed at the interfaces between the water globules of the disperse phase and the oil of the continuous phase. Other theories blame the high inherent viscosity of the crude and the presence of asphaltic and resinous constituents. Despite the severity of the problem and the diversity of theories as to its causes, efforts to reduce the BS&W content of such crudes below pipeline specifications frequently fail completely, causing the operator of the wells to resort to such expensive expedients as blending the high BS&W crude with a clean crude in order to reach specifications. In some instances, the BS&W content of the crude, even after treatment, remains so high that the crude must be considered unsuitable for normal refining. There has thus been a continuing need for a method which will break the emulsion of such crudes and accomplish a good separation of solids and water from the oil.